Transmission method and transmission apparatus

ABSTRACT

Of any one of a transmission method X of transmitting modulated signal A and modulated signal B including the same data from a plurality of antennas and a transmission method Y of transmitting modulated signal A and modulated signal B having different data from the plurality of antennas, a base station apparatus does not change the transmission method during data transmission and changes only the modulation scheme. The base station apparatus transmits modulated signal A and modulated signal B to a communication terminal apparatus using the determined transmission method and modulation scheme. In this way, it is possible to improve data transmission efficiency when transmitting data using the plurality of antennas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of application Ser. No. 13/590,779filed Aug. 21, 2012, which is a continuation application of Ser. No.13/176,459 filed Jul. 5, 2011, which is a continuation application ofSer. No. 10/562,555, filed Dec. 28, 2005, which is a 371 application ofPCT/JP2004/009572 filed Jun. 30, 2004, which is based on JapaneseApplication No. 2003-188898 filed Jun. 30, 2003 and Japanese ApplicationNo. 2004-190418 filed Jun. 28, 2004, the entire contents of each ofwhich are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a transmission method, transmissionapparatus and communication system for transmitting data from aplurality of antennas simultaneously.

BACKGROUND ART

Conventionally, a technology disclosed in “Space-Time Block Codes fromOrthogonal Design” IEEE Transactions on Information Theory, pp.1456-1467, vol. 45, no. 5, July 1999 is known as a transmission methodusing a plurality of antennas. Hereinafter, the contents disclosed inthis document will be explained using drawings.

FIG. 1 illustrates a conventional frame configuration. In this figure,transmission signal A and transmission signal B are signals transmittedfrom different antennas simultaneously. Transmission signal A andtransmission signal B are consist of a symbol group containing the samedata. SyA and SyB in the figure denote symbols and “*” denotes a complexconjugate. Transmission signal A is configured to form a frame of datasymbols in an order of SyA, to −SyB* and the transmission signal B isconfigured to form a frame of data symbols in an order of SyB to SyA*.The transmission signal A and transmission signal B are synchronizedwith each other and transmitted. For this reason, data symbols SyA andSyB are transmitted simultaneously and data symbols −SyB* and SyA* aretransmitted simultaneously.

FIG. 2 illustrates a conventional communication system. Transmissionapparatus 11 is provided with antenna 12 and antenna 13 and transmits,for example, transmission signal A shown in FIG. 1 from antenna 12 andtransmission signal B from antenna 13 to reception apparatus 21.Reception apparatus 21 receives the signals transmitted from theantennas of transmission apparatus 11 by antenna 22. The signal receivedby antenna 22 is a combination of transmission signal A and transmissionsignal B, and therefore the received signal is separated intotransmission signal A and transmission signal B and then demodulated.

In such a conventional communication system, transmission apparatus 11transmits transmission signal A from antenna 12 and transmission signalB from antenna 13 and the signals transmitted from the antennas arereceived by the reception apparatus via different channel fluctuations(h1(t) and h2(t)). A conventional communication system takes advantageof this and adopts frame configuration shown in FIG. 1, and therefore,it is possible to improve reception quality of reception apparatus 21.

However, in the above described conventional communication system, SyA*and −SyB* are demodulated as SyA, SyB at the reception apparatus, andinformation of SyA* and −SyB*are substantially the same with SyA, SyB.This means that the same information is transmitted twice, resulting inlow data transmission efficiency.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a communicationmethod, transmission apparatus and communication system for improvingdata transmission efficiency when transmitting data using a plurality ofantennas.

It is possible to attain the above described object with a transmissionapparatus provided with a plurality of antennas, by determining any oneof a first transmission method of transmitting a plurality of signalscontaining the same data from the plurality of antennas respectively anda second transmission method of transmitting a plurality of signalscontaining different data from the plurality of antennas respectivelybased on channel fluctuations between the transmitting and receivingsides and by determining, when determining any one of a plurality ofmodulation schemes, only a modulation scheme out of transmission methodsand modulation schemes from beginning to end of a communication.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a conventional frame configuration;

FIG. 2 illustrates a conventional communication system;

FIG. 3A illustrates frame configurations of modulated signal A andmodulated signal B according to transmission method X;

FIG. 3B illustrates frame configurations of modulated signal A andmodulated signal B according to transmission method Y;

FIG. 4 is a schematic diagram showing a communication system accordingto Embodiment 1 of the present invention;

FIG. 5 is a block diagram showing the configuration of a transmissionapparatus at a base station apparatus according to Embodiment 1 of thepresent invention;

FIG. 6 is a block diagram showing the configuration of a receptionapparatus at a communication terminal apparatus according to Embodiment1 of the present invention;

FIG. 7A illustrates that a received signal has arrived on a direct wave;

FIG. 7B illustrates that a received signal has arrived on only ascattered wave without including any direct wave;

FIG. 8 illustrates a sequence diagram of a communication procedure ofthe base station apparatus and communication terminal apparatusaccording to Embodiment 1 of the present invention;

FIG. 9 illustrates changes with time of a transmission method and amodulation scheme applied by the base station apparatus according toEmbodiment 1;

FIG. 10 illustrates a mode in which a transmission method and amodulation scheme are changed;

FIG. 11 illustrates the number of transmission bits per unit timeaccording to a combination of transmission method X and transmissionmethod Y, and each modulation scheme;

FIG. 12 illustrates an input/output characteristic of an amplifier;

FIG. 13 illustrates a sequence diagram of a communication procedure of abase station apparatus and communication terminal apparatus according toEmbodiment 2 of the present invention;

FIG. 14 illustrates changes with time of a transmission method andmodulation scheme applied by the base station apparatus according toEmbodiment 2;

FIG. 15A illustrates a frame configuration of modulated signal A andmodulated signal B according to transmission method X;

FIG. 15B illustrates a frame configuration of modulated signal A andmodulated signal B according to transmission method Y:

FIG. 16A illustrates a frame configuration of transmission method X;

FIG. 16B illustrates a frame configuration of transmission method Y;

FIG. 17 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 3 of the present invention;

FIG. 18 is a block diagram showing the configuration of a communicationterminal apparatus according to Embodiment 3 of the present invention;

FIG. 19 illustrates a sequence diagram of a communication procedure ofthe base station apparatus and communication terminal apparatusaccording to Embodiment 3 of the present invention;

FIG. 20 illustrates changes with time of a transmission method andmodulation scheme applied by the base station apparatus according toEmbodiment 3;

FIG. 21 illustrates a sequence diagram of a communication procedure of abase station apparatus and communication terminal apparatus according toEmbodiment 4 of the present invention;

FIG. 22 illustrates changes with time of a transmission method andmodulation scheme applied by the base station apparatus according toEmbodiment 4;

FIG. 23 illustrates a frame configuration when CDD is carried out using12 symbols;

FIG. 24 illustrates the configuration of a channel multiplexingcommunication system using a beam space mode represented by an eigenmodein an MIMO system;

FIG. 25 illustrates the configuration of a transmission apparatus of abase station apparatus according to Embodiment 6 of the presentinvention;

FIG. 26A illustrates a point-to-multi point type communication mode;

FIG. 26B illustrates a point-to-point type communication mode;

FIG. 26C illustrates a point-to-point type communication mode;

FIG. 27 illustrates an effect when a transmission method is changedaccording to the number of other communication parties;

FIG. 28 illustrates an effect when a transmission method is changedaccording to the number of other communication parties; and

FIG. 29 illustrates a sequence diagram showing a communication procedureof a base station apparatus and communication terminal apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the accompanied drawings, embodiments of thepresent invention will be explained below.

Embodiment 1

Frame Configuration

FIG. 3 illustrates frame configurations according to Embodiment 1 of thepresent invention. FIG. 3A illustrates the frame configurations ofmodulated signal A and modulated signal B according to transmissionmethod X and FIG. 3B illustrates the frame configurations of modulatedsignal A and modulated signal B according to transmission method Y.Channel condition estimation symbol 101 and radio wave propagationenvironment estimation symbol 103 are symbols for a reception apparatusof the other communication party to estimate a channel condition andcalled “pilot symbol”, “preamble”, “control symbol”, “predeterminedsymbol”, “unique word” or the like.

Transmission method reporting symbol 102 is a symbol showing atransmission method (X or Y), modulation scheme, error correcting schemeof a modulated signal transmitted from a base station apparatus.

Data symbol 104 is user information such as audio data, image data andcharacter data transmitted from the base station apparatus to acommunication terminal apparatus.

Transmission Method X and Transmission Method Y

Transmission method X is a transmission method disclosed in the abovedescribed document as in the case of the above described conventionalexample for transmitting data symbols including the same data(hereinafter referred to as “space-time coding”) from two antennas. As aspecific example, from among data symbols SyA, SyB, SyA*, −SyB* (“*”denotes a complex conjugate), modulated signal A is composed of datasymbols in an order of SyA and −SyB* and modulated signal B is composedof data symbols in an order of SyB, SyA*. On the other hand, informationaccording to transmission method Y is configured to form a frame fromdifferent data symbols. As a specific example, from among data symbolsSyA, SyB, SyC, SyD which are information with different contents,modulated signal A is composed of data symbols SyA and SyC and modulatedsignal B is composed of data symbols SyB and SyD.

Note that both transmission method X and transmission method Y shown inFIGS. 3A and 3B synchronize modulated signal A and modulated signal Bwith each other and transmit them. For example, according totransmission method X, data symbols −SyB* and SyA* are transmittedsimultaneously and according to transmission method Y, data symbols SyCand SyD are transmitted simultaneously. Furthermore, symbols of the sametype of modulated signal A and modulated, signal B are also transmittedsimultaneously.

FIG. 4 is a schematic diagram showing a communication system accordingto Embodiment 1 of the present invention. In this figure, base stationapparatus 201 is provided with antenna 202 and antenna 203 andcommunicates with communication terminal apparatus 251 via a radiochannel. Communication terminal apparatus 251 is provided with antenna252 and antenna 253. This figure shows a situation where base stationapparatus 201 is transmitting a signal to communication terminalapparatus 251.

Features of Transmission Method X and Transmission Method Y

Here, suppose a channel condition in a channel fluctuation betweenantenna 202 and antenna 252 is h11(t) and a channel condition in achannel fluctuation between antenna 202 and antenna 253 is h12(t).Likewise, suppose a channel condition between antenna 203 and antenna252 is h21(t) and a channel condition between antenna 203 and antenna253 is h22(t) Here, t denotes time. Channel conditions h11(t), h12(t),h21(t), h22(t) are estimated by communication terminal apparatus 251using channel condition estimation symbol 101 and radio wave propagationenvironment estimation symbol 103.

At this time, according to transmission method X, the following equationholds:

$\begin{matrix}{\begin{pmatrix}{R\; 1(i)} \\{R\; 1\left( {i + 1} \right)}\end{pmatrix} = {\begin{pmatrix}{h\; 11(i)} & {h\; 21(i)} \\{h\; 21*\left( {i + 1} \right)} & {{- h}\; 11*\left( {i + 1} \right)}\end{pmatrix}\begin{pmatrix}{SyA} \\{SyB}\end{pmatrix}}} & (1)\end{matrix}$

where R1(t) is the received signal of antenna 252 shown in FIG. 4.

As is appreciated from this equation, according to transmission methodX, data symbols SyA and SyB are repeatedly transmitted at times t=i andt=i+1. Here, a case where space-time block codes are used is explained,but it is also possible to use space-time trellis codes as exemplifiedin the following reference document. (Reference document: “Space-TimeBlock Codes for High Data Rate Wireless Communication: PerformanceCriterion and Code Construction” IEEE Transactions on InformationTheory, pp. 744-765, vol 44, no. 2, March 1998)

On the other hand, according to transmission method Y, the followingequation holds:

$\begin{matrix}{\begin{pmatrix}{R\; 1(i)} \\{R\; 2(i)}\end{pmatrix} = {\begin{pmatrix}{h\; 11(i)} & {h\; 12(i)} \\{h\; 21(i)} & {h\; 22(i)}\end{pmatrix}\begin{pmatrix}{SyA} \\{SyB}\end{pmatrix}}} & (2)\end{matrix}$

where R1(t), R2(t) denote the received signals of antennas 252 and 253shown in FIG. 4.

As is appreciated from this equation, according to transmission methodY, data symbols SyA and SyB are transmitted only at time t=i.

As shown above, when transmission method X is compared with transmissionmethod Y, transmission method X has a lower transmission rate thantransmission method Y, yet has good reception quality. On the contrary,transmission method Y has a higher transmission rate than transmissionmethod X, yet has a tendency that reception quality deterioratesconsiderably. Especially, transmission method Y has a property ofdeteriorating reception quality severely when a direct wave is received.For this reason, it may be considered that transmission method X is usedwhen a direct wave is received and transmission method Y is used when adirect wave is not received.

Thus, determining transmission method X having high error resistance,hence high reception quality or transmission method Y having a hightransmission rate according to the state of a channel fluctuation makesit possible to improve both reception quality and the transmission rate.That is, by switching the modulation scheme as well as by switchingbetween transmission method X and transmission method Y, it is possibleto further improve both reception quality and the transmission rate.

Configuration of Transmission Apparatus at Base Station Apparatus 201

FIG. 5 is a block diagram showing the configuration of a transmissionapparatus at base station apparatus 201 according to Embodiment 1 of thepresent invention. In this figure, frame generation instruction section401 determines a transmission method (X or Y) and modulation scheme(e.g., any one of QPSK, 16QAM and 64QAM) based on the transmissionmethod request information and modulation scheme request informationtransmitted from communication terminal apparatus 251 and instructs thedetermined contents to data sequence generation section 402,transmission processing section 403 and transmission processing section404 by means of frame generation instruction signal S1.

Data sequence generation section 402 generates transmission digitalsignal S2 of modulated signal A and transmission digital signal S3 ofmodulated signal B in the frame configuration shown in FIG. 3 from thetransmission digital signal in accordance with the instruction fromframe generation instruction section 401. Generated transmission digitalsignal S2 of modulated signal A is output from data sequence generationsection 402 to transmission processing section 403 and generatedtransmission digital signal S3 of modulated signal B is output from datasequence generation section 402 to transmission processing section 404.

Transmission processing section 403 and transmission processing section404 carry out transmission processing on transmission digital signal S2of modulated signal A output from data sequence generation section 402and transmission digital signal S3 of modulated signal B output fromdata sequence generation section 402, respectively according to theinstructions from frame generation instruction section 401. Sincetransmission processing section 403 and transmission processing section404 have the same internal configuration, the configuration oftransmission processing section 403 will be explained below.

Modulation section 4031 is capable of modulating under a plurality ofmodulation schemes and modulates transmission digital signal S2 ofmodulated signal A output from data sequence generation section 402under the modulation scheme instructed from frame generation instructionsection 401. Modulated signal S4 is output from modulation section 4031to spreading section 4032.

Spreading section 4032 multiplies signal S4 output from modulationsection 4031 by a spreading code and outputs spread modulated signal Ato radio section 4033 and radio section 4033 carries out predeterminedradio processing (D/A conversion or up-conversion or the like) on spreadsignal S5 and outputs signal S6 after the radio processing to amplifier4034.

Amplifier 4034 amplifies the power of signal 36 output from radiosection 4033 and transmits power-amplified signal S7 from antenna 202 tocommunication terminal apparatus 251.

Configuration of Reception Apparatus at Communication Terminal Apparatus251

FIG. 6 is a block diagram showing the configuration of a receptionapparatus at communication terminal apparatus 251 according toEmbodiment 1 of the present invention. In this figure, antenna 252receives signal S51 combining the signals transmitted from antenna 202and antenna 203 of base station apparatus 201 and radio section 501carries out predetermined radio processing (down-conversion and A/Dconversion or the like) on signal S51 received by antenna 252 andoutputs signal S52 after the radio processing to despreading section502.

Despreading section 502 multiplies signal S52 output from radio section501 by a spreading code and carries out despreading. Despread signal S53is output from despreading section 502 to frame synchronization section503, first channel fluctuation estimation section 504, second channelfluctuation estimation section 505, demodulation section 510 andreception field intensity estimation section 511.

Frame synchronization section 503 achieves frame synchronization betweenmodulated signal A and modulated signal B based on signal S53 outputfrom despreading section 502 and signal S56 output from despreadingsection 507 and forms timing signal S57. Timing signal S57 is outputfrom frame synchronization section 503 to first channel fluctuationestimation sections 504 and 508, second channel fluctuation estimationsections 505 and 509 and demodulation section 510.

First channel fluctuation estimation section 504 estimates a channelfluctuation of modulated signal A, that is, estimates a channelcondition according to timing signal S57 output from framesynchronization section 503 using channel condition estimation symbol101 of modulated signal A and radio wave propagation environmentestimation symbol 103 out of signal S53 output from despreading section502. The estimated channel fluctuation information of modulated signal Ais output as channel fluctuation estimation signal S58 from firstchannel fluctuation estimation section 504 to demodulation section 510and eigenvalue calculation section 512. Channel fluctuation estimationsignal S58 of modulated signal A corresponds to h11(t) of Equation (2).

Second channel fluctuation estimation section 505 estimates a channelfluctuation of modulated signal B (channel condition) according totiming signal S57 output from frame synchronization section 503 usingchannel condition estimation symbol 101 of modulated signal B and radiowave propagation environment estimation symbol 103 out of signal 53output from despreading section 502. The estimated channel fluctuationinformation of modulated signal B is output as channel fluctuationestimation signal S59 from second channel fluctuation estimation section505 to demodulation section 510 and eigenvalue calculation section 512.Channel fluctuation estimation signal S59 of modulated signal Bcorresponds to h12(t) of Expression (2).

Signal 554 received by antenna 253 is subjected to processing similar tothat described above by radio section 506, despreading section 507,first channel fluctuation estimation section 508 and second channelfluctuation estimation section 509, and therefore detailed explanationsthereof will be omitted. Note that channel fluctuation estimation signalS60 output from first channel fluctuation estimation section 508 todemodulation section 510 corresponds to h21(t) of Equation (2) andchannel fluctuation estimation signal S61 output from second channelfluctuation estimation section 509 to demodulation section 510corresponds to h22(t) of Equation (2).

Demodulation section 510 demodulates signals S53 and S56 output fromdespreading section 502 and despreading section 507 according to timingsignal S57 output from frame synchronization section 503 using channelfluctuation estimation signals S58, S59, S60 and S61 output from firstchannel fluctuation estimation sections 504 and 508, second channelfluctuation estimation sections 505 and 509 and obtains a receiveddigital signal of modulated signal A and a received digital signal ofmodulated signal B. At this time, demodulation section 510 acquires atransmission method (X or Y), modulation scheme and error correctingscheme of the signal from transmission method reporting symbol 102 ofsignals S53, S56 output from despreading section 502 and despreadingsection 507 and demodulates the data symbols according to the acquiredcontents.

Reception field intensity estimation section 511 estimates receptionfield intensity based on signals S53 and S56 output from despreadingsection 502 and despreading section 507 and outputs the estimationresult as reception field intensity estimation signal S62 to modulationscheme determining section 513 and transmission method determiningsection 514. The reception field intensity referred to here meanseffective carrier power. Furthermore, with regard to the channelfluctuation estimation sections such as first channel fluctuationestimation sections 504, 508 and second channel fluctuation estimationsections 505, 509 and reception field intensity estimation section 511,any one or both of the channel fluctuation estimation sections andreception field intensity estimation section 511 function as the channelfluctuation estimation section.

When channel fluctuation information output from first channelfluctuation estimation sections 504 and 508 and second channelfluctuation estimation sections 505 and 509 is assumed to be a channelmatrix as shown in Equation (2), eigenvalue calculation section 512calculates the eigenvalue. The calculated eigenvalue is output aseigenvalue signal S63 from eigenvalue calculation section 512 tomodulation scheme determining section 513 and transmission methoddetermining section 514.

Modulation scheme determining section 513 as a modulation schemerequesting section determines the modulation scheme to be requested frombase station apparatus 201 based on reception field intensity estimationsignal S62 output from reception field intensity estimation section 511and eigenvalue signal S63 output from eigenvalue calculation section 512and outputs the modulation scheme as modulation scheme requestinformation. Note that the modulation scheme may also be determined onlybased on reception field intensity and in this case, influences on thetransmission rate and transmission quality are small.

Transmission method determining section 514 as a transmission methodrequesting section determines transmission method X or transmissionmethod Y applied by base station apparatus 201 when a communication isstarted based on eigenvalue signal S63 output from eigenvaluecalculation section 512 and estimation signal S62 (reception fieldintensity) output from reception field intensity estimation section 511.The determined information is output from communication terminalapparatus 251 as transmission method request information. Taking thecase of Equation (2) as an example to explain more specifically,eigenvalue signal S63 output from eigenvalue calculation section 512includes two eigenvalues and a difference in the magnitude of eigenvalueis calculated assuming that these two eigenvalues are λ1, λ2(|λ1(t)|>|λ2(t)|). That is, |λ1(t)|²−|λ2(t)|² is calculated. When thisdifference is greater than a predetermined value, transmission method Xis determined assuming that a direct wave is received. On the contrary,when this difference is smaller than the predetermined value,transmission method Y is determined assuming that only a scattered waveincluding no direct wave is received. In this respect, the calculationresult of |λ1(t)|²−|λ2(t)|² reflects the state of a probability densitydistribution of eigenvalues.

Method of Deciding Whether or not Received Signal is Arriving on DirectWave

The method of deciding whether or not a received signal is arriving on adirect wave will be explained using FIG. 7. First, tan⁻¹(Q/I) iscalculated from an I component and a Q component of a received basebandsignal. FIG. 7 is a figure expressing tan⁻¹(Q/I) on the horizontal axisand probability density on the vertical axis. FIG. 7A illustrates a casewhere a direct wave has been received and a high probability that a peakappears in the phase of a direct wave is high. On the other hand, FIG.7B illustrates a case where only a scattered wave including no directwave has been received and probability that a peak appears is low. Inthis way, it is possible to determine whether or not a direct wave hasbeen received by calculating a probability density of tan⁻¹(Q/I) anddeciding how it is distributed.

Furthermore, two eigenvalues of a 2×2 matrix (hereinafter referred to as“channel matrix”) expressed by the channel condition component of abovedescribed Equation (2) are obtained and if the eigenvalues are expressedby λ1, λ2 (|λ1|>|λ2|), the presence or absence of a received direct waveis reflected in the relationship between λ1 and λ2. For this reason, itis possible to decide whether or not a direct wave has been receivedbased on an eigenvalue of a channel matrix. More specifically, it ispossible to express the magnitude of the eigenvalue with a probabilitydensity distribution and the reception quality depends on thedistribution of the eigenvalue, and therefore it is possible to decidewhether or not reception quality corresponds to the quality when adirect wave has been received based on the distribution of theeigenvalue.

Transmission Method and Modulation Scheme Applied to Transmission MethodReport Symbol

Transmission method reporting symbol 102 is the information to reportthe transmission method of a modulated signal, modulation scheme anderror correcting scheme. It is difficult to demodulate data unless thistransmission method reporting symbol 102 is demodulated correctly andtherefore, it is desirable to transmit transmission method reportingsymbol 102 using transmission method X and BPSK as the modulationscheme. Furthermore, it is further desirable to incorporate errorcorrection. This makes it possible to improve the error resistance oftransmission method reporting symbol 102 and also improve thedemodulation accuracy of this symbol and therefore, communicationterminal apparatus 251 is capable of acquiring the transmission method,modulation scheme and error correcting scheme correctly. Therefore, basestation apparatus 201 can transmit information about the transmissionmethod, modulation scheme and error correcting scheme of data symbol 104to communication terminal apparatus 251 correctly and avoid thesituation where communication terminal apparatus 251 cannot demodulatedata.

Furthermore, for example, even when transmission method Y is determinedat the beginning of a communication, it is possible to transmit themodulation scheme and error correcting scheme accurately by transmittinga transmission method report symbol using transmission method X, whichresult in improving the reception quality. Since both transmissionmethod X and transmission method Y have two systems of modulated signalsto be transmitted, the transmission method is changed, that is,transmission method Y is changed to transmission method X withoutchanging the number of antennas of the transmission apparatus of thebase station apparatus. Therefore, no change is involved in the hardwareof the radio apparatus and a transmission method reporting symbol istransmitted accurately and reception quality of the data can be improvedeasily.

Operations of Base Station Apparatus 201 and Communication TerminalApparatus 251

FIG. 8 is a sequence diagram showing the communication procedure of basestation apparatus 201 and communication terminal apparatus 251 accordingto Embodiment 1 of the present invention. In this figure, in step(hereinafter abbreviated as “ST”) 601, communication terminal apparatus251 requests base station apparatus 201 to start a communication andbase station apparatus 201 receives this request.

In ST602, base station apparatus 201 reports to communication terminalapparatus 251 that a request to start a communication is received inST601. At this time, channel condition estimation symbol 101 shown inFIG. 3 is also transmitted together.

In ST603, communication terminal apparatus 251 estimates a channelcondition using channel condition estimation symbol 101 transmitted inST602, determines the transmission method (X or Y) of the modulatedsignal and modulation scheme transmitted by base station apparatus 201based on the eigenvalue of the channel matrix expressed by Equation (2)and requests the determined transmission method and modulation schemefrom base station apparatus 201. Base station apparatus 201 receivesthis request.

In ST604, base station apparatus 201 determines the transmission methodand modulation scheme based on the requests for the transmission methodand modulation scheme transmitted from communication terminal apparatus251 and transmits the determined transmission method and modulationscheme to communication terminal apparatus 251 using transmission methodreporting symbol 102.

In ST605, base station apparatus 201 transmits radio wave propagationenvironment estimation symbol 103 and data symbol 104 to communicationterminal apparatus 251 using the transmission method and modulationscheme determined in ST604 according to the frame configuration shown inFIG. 3

In ST606, during a communication with base station apparatus 201,communication terminal apparatus 251 determines only the modulationscheme again based on radio wave propagation environment estimationsymbol 103 and requests the determined modulation scheme from basestation apparatus 201. Base station apparatus 201 receives this request.

In ST607, base station apparatus 201 determines only the modulationscheme again based on the request transmitted from communicationterminal apparatus 251 and notifies the modulation scheme ofcommunication terminal apparatus 251 using transmission method reportingsymbol 102.

In ST608, base station apparatus 201 transmits radio wave propagationenvironment estimation symbol 103 and data symbol 104 to communicationterminal apparatus 251 using the modulation scheme determined in ST607according to the frame configuration shown in FIG. 3.

In ST609, base station apparatus 201 reports an end of communication tocommunication terminal apparatus 251 and communication terminalapparatus 251 receives this report and finishes the communication.

Method of Changing Transmission Method and Modulation Scheme

In the above described series of communication procedures, FIG. 9 showshow the transmission method and modulation scheme applied by basestation apparatus 201 change with time-shift. Here, three modulationschemes QPSK, 16QAM, 64QAM are supposed to be used. In this figure, itis supposed that a communication between base station apparatus 201 andcommunication terminal apparatus 251 starts at time t0 and transmissionmethod X and QPSK are used from time t1 to t2. At time t2, only themodulation scheme is changed from QPSK to 16QAM and from time t2 to t3,transmission method X and 16QAM are used. Furthermore, at time t3, onlythe modulation scheme is changed again from 16QAM to 64QAM. From time t3to t4, transmission method X and 64QAM are used and the communicationends at time t5.

Furthermore, at time t6, when base station apparatus 201 andcommunication terminal apparatus 251 start a communication, transmissionmethod Y and 64QAM are supposed to be used from time t7 to t8. At timet8, only the modulation scheme is changed from 64QAM to 16QAM andtransmission method Y and modulation scheme 16QAM are used from time t8to t9. Furthermore, at time t9, only the modulation scheme is changedagain from 16QAM to QPSK. From time t9 to t10, transmission method Y andQPSK are used and the communication ends at time t11.

Note that the changes of the modulation scheme at times t2, t3, t8 andt9 are the results of reflecting the modulation scheme request in ST606shown in FIG. 8 and the modulation scheme is changed according to theradio wave propagation environment.

Thus, the transmission method is determined at the beginning of thecommunication and the transmission method is not changed from start toend of the communication and only the modulation scheme is changed.

Method of changing transmission method and modulation scheme other thanmethods shown in FIG. 9

In addition to the method of changing the transmission method andmodulation scheme shown in FIG. 9, the change method shown in FIG. 10can also be considered. FIG. 10 will be explained below.

In FIG. 10, a communication between the base station apparatus andcommunication terminal apparatus starts at time t0 and transmissionmethod X and QPSK are used from time t1 to t2. At time t2, transmissionmethod X is changed to transmission method Y and the modulation schemeis changed from QPSK to 16QAM. At time t3, transmission method Y ischanged to transmission method X and the modulation scheme is changedfrom 16QAM to 64QAM. At time t4, only the transmission method is changedfrom X to Y and at time t5, only the modulation scheme is changed from64QAM to 16QAM. At time t7, the communication ends.

In this way, both the transmission method and modulation scheme may bechanged during a communication in accordance with the radio wavepropagation environment. However, such a change method increases thenumber of combinations (hereinafter simply referred to as“combinations”) that can be selected when the change takes place, whichresults in a more complicated system. That is, when one out of manycombinations is selected, it is necessary to estimate a radio wavepropagation environment with high accuracy and a combination which isnot suitable for the radio wave propagation environment may be selectedunless high accuracy estimation is performed, which may deterioratereception quality.

Furthermore, if the estimation accuracy of the radio wave propagationenvironment is improved, a combination suitable for the radio wavepropagation environment may be selected, but when the communicationterminal apparatus performs high accuracy estimation, the stability ofthe system depends on the estimation accuracy of the radio wavepropagation environment of the communication terminal apparatus and itis more difficult to reduce the size of the terminal apparatus andreduce power consumption.

Therefore, as shown in FIG. 9, only changing the modulation schemewithout changing the transmission method during a communication willsave the base station apparatus and communication terminal apparatus acomplicated communication procedure. Furthermore, it is also possible toalleviate the estimation accuracy of the radio wave propagationenvironment of the communication terminal apparatus, reduce the size andpower consumption of the communication terminal apparatus and preventthe processing load of the overall system increasing.

In this respect, even when the transmission method is not changed duringa communication, the propagation model does not change drastically.Furthermore, transmission method Y has a high data transmission rate,but its propagation model has a considerable influence on the receptionquality.

Modulation scheme to be combined with transmission method X ortransmission method Y

FIG. 11 illustrates the number of transmission bits per unit time by acombination of transmission method X and transmission method Y and eachmodulation scheme. Transmission method Y can transmit twice as manytransmission bits as those of transmission method X under eachmodulation scheme. Here, it is necessary to realize a combination oftransmission method X with 4096QAM in order that transmission method Xcan also obtain the same amount of transmission bits per unit timetransmitted as transmission method Y.

However, the reception quality when 4096QAM is adopted for transmissionmethod X is lower than the reception quality of when 64QAM is adoptedfor transmission method Y. For this reason, to improve both thereception quality and transmission rate, it is not desirable to realize4096QAM using transmission method X.

Furthermore, input and output characteristics of amplifiers 4034 and4044 of base station apparatus 201 shown in FIG. 5 will be consideredusing FIG. 12. FIG. 12 illustrates an input and output characteristic ofthe amplifier. In this figure, it is premised that the horizontal axisshows an input level and the vertical, axis shows an output level, theinput range of QPSK is A1, the input range of 64QAM is A2 and the inputrange of 4096QAM is A3. In addition, two different input and outputcharacteristics are shown with a solid line and dotted linerespectively. Suppose the amplifier having the input and outputcharacteristic shown with the solid line (hereinafter referred to as“amplifier P1”) has a range of A2 and the amplifier having the input andoutput characteristic shown with the dotted line (hereinafter referredto as “amplifier P2”) has a range of A3. Note that if the modulationscheme is unchanged, the amplitude variation range of a modulatedsignal, that is, the input range is also unchanged irrespective of thetransmission method. Furthermore, the amplitude variation range of amodulated signal generally increases as the number of modulated M-aryindex increases.

Using amplifier P1 is sufficient if the maximum number of modulatedM-ary index is 64QAM with transmission method Y. On the contrary, inorder that transmission method X realizes the transmission rate that isrealized by using a combination of transmission method Y and 64QAM, itis necessary to use the modulation scheme of 4096QAM, and in this case,amplifier P2 must be used. The output characteristic of amplifier P2extends over a wider range of the output level than the outputcharacteristic of amplifier P1 and the reception apparatus needs toprocess a signal having a wider range of variation, and therefore thereception apparatus needs to secure linearity of this signal, whichcomplicates the circuit configuration.

Furthermore, since amplifier P2 consumes greater power than amplifierP1, it has lower power efficiency and has the larger scale of theamplifier itself.

From this, it is desirable to equalize the maximum number of modulatedM-ary index of the modulation scheme to be combined with transmissionmethod X or transmission method Y. This makes it possible to suppresspower consumption of the transmission apparatus and simplify the circuitconfiguration of the reception apparatus.

Maximum value of number of modulated M-ary index when the number oftransmission antennas is 4

When the above described case with two transmission antennas is changedto a case with four transmission antennas, where modulated signals aretransmitted from four transmission antennas, it is not necessary for thereception apparatus to process a signal having a wide variation range bysetting a smaller maximum value of the number of modulated M-ary indexwith four transmission antennas than the maximum value of the number ofmodulated M-ary index with two transmission antennas, and therefore itis possible to simplify the circuit configuration of the receptionapparatus.

Explanations of the above described number of modulated M-ary index arenot limited to a single carrier scheme but the same applies to a casewhere a multicarrier scheme including an OFDM scheme is used.Furthermore, a spread spectrum scheme may be used or may not be used.

Thus, according to this embodiment, the base station apparatus andcommunication terminal apparatus are provided with a plurality ofantennas respectively, the base station apparatus determines any one oftransmission method X whereby modulated signal A and modulated signal Bincluding the same data are transmitted from a plurality of antennas andtransmission method Y whereby modulated signal A and modulated signal Bincluding different data are transmitted from a plurality of antennas atthe beginning of a communication, does not change the transmissionmethod during the communication and only changes the modulation scheme,and can thereby improve both the data transmission rate and transmissionquality.

In this embodiment, the communication terminal apparatus estimates apropagation model using channel condition estimation symbols transmittedfrom the base station apparatus at the beginning of a communication andrequests a transmission method. And it is also possible that thecommunication terminal apparatus receives radio wave propagationenvironment estimation symbols and data symbols transmitted by the basestation apparatus when the base station apparatus is communicating withthe other communication terminal apparatus and requests the transmissionmethod at the beginning of a communication. This eliminates thenecessity for inserting channel condition estimation symbols into aframe, and can thereby further increase the data transmission rate.

Furthermore, in this embodiment, the communication terminal apparatusdetermines a transmission method and modulation scheme based oneigenvalues and reception field intensity, but the present invention isnot limited to this, and can also determine a transmission method andmodulation scheme based on at least one of a bit error rate, packet lossrate and frame error rate, and reception field intensity. For example,transmission method X may be determined when the reception fieldintensity is strong, but the bit error rate is high.

Embodiment 2

Embodiment 1 has explained the case where the transmission method is notchanged during a communication, but this embodiment will explain a casewhere a transmission method is changed during a communication.

The configurations of a base station apparatus and communicationterminal apparatus in this embodiment are the same as those ofEmbodiment 1, and therefore FIG. 5 and FIG. 6 will be used again anddetailed explanations thereof will be omitted.

FIG. 13 illustrates a sequence diagram of a communication procedure ofthe base station apparatus and communication terminal apparatusaccording to Embodiment 2 of the present invention. However, ST1101 toST1108 in this figure are the same as ST601 to ST608 in FIG. 8 andST1111 to ST1114 are the same as ST605 to ST608, and therefore detailedexplanations thereof will be omitted.

In ST1109, the communication terminal apparatus estimates a channelcondition using channel condition estimation symbols transmitted fromthe base station apparatus and determines a transmission method andmodulation scheme applied by the base station apparatus during acommunication based on the eigenvalues of the channel matrix shown byEquation (2) in Embodiment 1. The communication terminal apparatusrequests the determined transmission method and modulation scheme fromthe base station apparatus. The base station apparatus receives thisrequest.

In ST1110, the base station apparatus determines a transmission methodand modulation scheme based on the request transmitted from thecommunication terminal apparatus and notifies the communication terminalapparatus of the determined combination using transmission method reportsymbols.

In ST1115, the base station apparatus reports end of a communication tothe communication terminal apparatus and the communication terminalapparatus receives this report, and then the communication ends.

In such a series of communication procedures, FIG. 14 illustrateschanges with time-shift of a transmission method and modulation schemeapplied by the base station apparatus. Here, three modulation schemesQPSK, 16QAM, 64QAM are supposed to be used. In this figure, suppose acommunication between the base station apparatus and communicationterminal apparatus starts at time t0 and transmission method X and QPSKare used from time t1 to t2. At time t2, only the modulation scheme ischanged from QPSK to 16QAM and transmission method X and 16QAM are usedfrom time t2 to t3. Furthermore, at time t3, only the modulation schemeis changed again from 16QAM to 64QAM. Transmission method X and 64QAMare used from time t3 to t4.

At time t4, the communication terminal apparatus requests to change thetransmission method and modulation scheme, requesting to change thetransmission method to transmission method Y and maintain the modulationscheme of 64QAM.

At time t5, the transmission method is changed during a communicationfrom transmission, method X to transmission method Y and the modulationscheme is kept to 64QAM Transmission method Y and 64QAM are used fromtime t5 to t6.

At time t6, only the modulation scheme is changed from 64QAM to 16QAMand transmission method Y and modulation scheme 16QAM are used from timet6 to t7. Furthermore, at time 7V, only the modulation scheme is changedagain from 16QAM to QPSK. Transmission method Y and QPSK are used fromtime t7 to t8 and the communication ends at time t9.

In this way, by changing the transmission method during a communicationat predetermined time intervals, it is possible to respond to changes ofa propagation path model. Note that the predetermined time interval issuch an interval that transmission methods are not changedunnecessarily.

In this way, according to this embodiment, when a communication timetakes a long time, the propagation model may change, and therefore, itis possible to improve both reception quality and the increase oftransmission rate even when the propagation model is changed during thecommunication by changing the transmission method during acommunication.

This embodiment may also be adapted so as not to estimate a propagationmodel at the start of a communication, to forcibly start a communicationusing transmission method X and estimate the propagation model usingradio wave propagation environment estimation symbols during thecommunication. This eliminates the necessity for inserting channelcondition estimation symbols in a frame, and can thereby furtherincrease the data transmission rate.

Furthermore, Embodiment 1 and Embodiment 2 have explained the spreadspectrum communication scheme, but the present invention is not limitedto this and can be likewise implemented under a single carrier schemewith the spreading section removed or under an OFDM scheme.

Embodiment 3

Embodiment 1 explains the case of the spread spectrum communicationscheme, but Embodiment 3 will explain a case where a transmission methodand modulation scheme are fixed at the beginning of a communicationunder an OFDM scheme.

FIG. 15 illustrates the frame configuration of Embodiment 3 of thepresent invention. Components common to FIG. 15 and FIG. 3 are assignedthe same reference numerals as those in FIG. 3 and detailed explanationsthereof will be omitted. As shown in FIG. 15, the OFDM scheme is toarrange symbols not only in a time direction but also in a frequencydirection, and here, the number of carriers is supposed to be 4. On eachcarrier, transmission method reporting symbol 102, radio wavepropagation environment estimation symbol 103 and data symbol 104 arearranged in that order.

FIG. 15A illustrates the frame configurations of modulated signal A andmodulated signal B using transmission method X. Focused on carrier 1, ithas the same arrangement of data symbols as an arrangement shown in FIG.3A and transmits data symbols in such an arrangement. Data symbols withthe same reference numerals as those of carrier 1 are also arranged oncarriers 2 to 4, which transmit the arranged data symbols.

FIG. 15B shows the frame configurations of modulated signal A andmodulated signal B using transmission method Y. Focused on carrier 1, ithas the same arrangement of data symbols as that shown in FIG. 3B andcarrier 1 transmits data symbols with different information contents.Data symbols with different information contents are also arranged oncarriers 2 to 4 as in the case of carrier 1 and carriers 2 to 4 transmitthe arranged data symbols.

FIG. 15 has shown the case of an OFDM scheme in which data symbols arecoded in a time area, but as shown in FIG. 16, this embodiment is alsoapplicable to a case of an OFDM scheme in which data symbols are codedin a frequency area. FIG. 16A shows the frame configuration oftransmission method X and FIG. 16B shows the frame configuration oftransmission method Y. At this time, in antenna 252 shown in FIG. 4,assuming that a received signal on carrier 1 and at time t is R1(t,1)and a received signal on carrier 2 and at time t is R1(t,2) Then, thefollowing equation holds:

$\begin{matrix}{\begin{pmatrix}{R\; 1\left( {i,1} \right)} \\{R\; 1\left( {i,2} \right)}\end{pmatrix} = {\begin{pmatrix}{h\; 11(i)} & {h\; 21(i)} \\{h\; 21*(i)} & {{- h}\; 11*(i)}\end{pmatrix}\begin{pmatrix}{SyA} \\{SyB}\end{pmatrix}}} & (3)\end{matrix}$

Similar coding can also be applied to carrier 3 and carrier 4.

FIG. 17 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 3 of the present invention. Note thatcomponents of FIG. 17 common to FIG. 5 are assigned the same referencenumerals as those in FIG. 5 and detailed explanations thereof will beomitted. In this figure, data sequence generation section 1401 generatestransmission digital signal S72 of modulated signal A and transmissiondigital signal S73 of modulated signal B corresponding to the frameconfiguration shown in FIG. 15 from a transmission digital signal inaccordance with an instruction (frame generation instruction signal S71)from frame generation instruction section 401. Generated transmissiondigital signal S72 of modulated signal A is output from data sequencegeneration section 1401 to transmission processing section 1402 andgenerated transmission digital signal S73 of modulated signal B isoutput to transmission processing section 1405.

Transmission processing section 1402 and transmission processing section1405 carry out transmission processing on transmission digital signalS72 of modulated signal A output from data sequence generation section1401 and transmission digital signal, S73 of modulated signal B outputfrom data sequence generation section 1401 respectively in accordancewith instructions from frame generation instruction section 401. Sincetransmission processing section 1402 and transmission processing section1405 have the same internal configuration, only the internalconfiguration of transmission processing section 1402 will be explained.

S/P conversion section 1403 converts serial signal S74 output frommodulation section 4031 to parallel signal S75 and outputs convertedparallel signal S75 to IDFT section 1404.

IDFT section 1404 performs an Inverse Discrete Fourier Transform onparallel signal S75 output from S/P conversion section 1403 and therebyforms OFDM signal S76 and outputs formed OFDM signal S76 to radiosection 4033.

FIG. 18 is a block diagram showing the configuration of a communicationterminal apparatus according to Embodiment 3 of the present invention.However, components of FIG. 18 common to FIG. 6 are assigned the samereference numerals as those in FIG. 6 and detailed explanations thereofwill be omitted.

Radio section 501 carries out predetermined radio processing(down-conversion and A/D conversion or the like) on signal S90 receivedby antenna 252 and outputs signal S91 after the radio processing to DFTsection 1501 and reception field intensity estimation section 1509.

DFT section 1501 performs a Discrete Fourier Transform on signal S91output from radio section 501 and outputs signal S92 after theconversion to first channel fluctuation estimation section 1502, secondchannel fluctuation estimation section 1503 and demodulation section1507.

Using radio wave propagation environment estimation symbols of modulatedsignal A out of signal S92 output from DFT section 1501, first channelfluctuation estimation section 1502 estimates a channel fluctuation ofmodulated signal A, that is, estimates a channel condition. The channelfluctuation information of estimated modulated signal A is output fromfirst channel fluctuation estimation section 1502 to demodulationsection 1507 as channel fluctuation estimation signal S93. Using radiowave propagation environment estimation symbols of modulated signal Bout of signal S92 output from DFT section 1501, second channelfluctuation estimation section 1503 estimates a channel fluctuation ofmodulated signal B (channel condition). The estimated channelfluctuation information of modulated signal B is output from secondchannel fluctuation estimation section 1503 to demodulation section 1507as channel fluctuation estimation signal S94, Channel fluctuationsignals S93 and S94 output from first channel fluctuation estimationsection 1502 and second channel fluctuation estimation section 1503include channel fluctuation information on carriers 1 to 4.

Signal S95 received by antenna 253 is subjected to processing similar tothe above described processing by radio section 506, DFT section 1504,first channel fluctuation estimation section 1505 and second channelfluctuation estimation section 1506, and therefore detailed explanationsthereof will be omitted.

Demodulation section 1507 demodulates signals S92 and S97 output fromDFT section 1501 and DFT section 1504 using channel fluctuationinformation S93, S94, S98, S99 output from first channel fluctuationestimation sections 1502 and 1505 and second channel fluctuationestimation sections 1503 and 1506. At this time, demodulation section1507 acquires a transmission method (X or Y) of the signal, modulationscheme and error correcting scheme from transmission method reportsymbols of signals S92 and S97 output from DFT section 1501 and DFTsection 1504, demodulates data symbols in accordance with the acquiredcontents and obtains received digital signal S100 of modulated signal Aand received digital signal S101 of modulated signal B. Demodulation isperformed based on relation equations of Equation (1) and Equation (2).The demodulated signal is output from demodulation section 1507 asreceived digital signals S100 and S101 and output to reception qualityestimation section 1508 as well.

Reception quality estimation section 1508 calculates a bit error rate,packet loss rate, frame error rate or the like based on signals S100 andS101 output from demodulation section 1507 and estimates receptionquality according to them. The estimation result is output fromreception quality estimation section 1508 to transmission methoddetermining section 1510 and modulation scheme determining section 1511as reception quality estimation signal S102

Reception field intensity estimation section 1509 estimates receptionfield intensity based on signals S91 and S96 output from radio section501 and radio section 506 and outputs the estimation result totransmission method determining section 1510 and modulation schemedetermining section 1511 as reception field intensity estimation signalS103.

Transmission method determining section 1510 determines transmissionmethod X or transmission method Y to be requested from the base stationapparatus based on reception quality estimation signal S102 output fromreception quality estimation section 1508 and reception field intensityestimation signal S103 output from reception field intensity estimationsection 1509 at a predetermined timing which will be described later andoutputs the transmission method as transmission method requestinformation. For example, transmission method determining section 1510determines transmission method X when the reception field intensity issecured, yet the reception quality cannot be secured, while determinestransmission method Y when the reception quality for the reception fieldintensity can be secured sufficiently.

Modulation scheme determining section 1511 determines a modulationscheme to be requested from the base station apparatus at apredetermined timing which will be described later based on receptionquality estimation signal S102 output from reception quality estimationsection 1508 and reception field intensity estimation signal S103 outputfrom reception field intensity estimation section 1509. The determinedscheme is output from the communication terminal apparatus as modulationscheme request information. The modulation scheme request informationand transmission method request information are transmitted to the basestation apparatus.

Next, the operations of the base station apparatus and communicationterminal apparatus having the above described configurations will beexplained. FIG. 9 illustrates a sequence diagram of a communicationprocedure of a base station apparatus and communication terminalapparatus according to Embodiment 3 of the present invention. In thisfigure, in ST1601, the communication terminal apparatus requests thebase station apparatus to start a communication and the base stationapparatus receives this request.

In ST1602, the base station apparatus receives the communication startrequest sent in ST1601 and transmits radio wave propagation environmentestimation symbols and data symbols to the communication terminalapparatus using transmission method X and under a modulation scheme ofBPSK. This makes it possible to improve reception quality of datasymbols immediately after a communication is started and realize highdemodulation accuracy at the communication terminal apparatus.

Following ST1603 to ST1609 correspond to ST603 to ST609 in FIG. 8, andtherefore detailed explanations thereof will be omitted.

FIG. 20 illustrates a transmission method and modulation scheme appliedby the base station apparatus changing with time-shift in such a seriesof communication procedures. Here, suppose three modulation schemesQPSK, 16QAM, 64QAM are used. In this figure, a communication between thebase station apparatus and communication terminal apparatus starts attime t0 and transmission method X and BPSK are forcibly used from timet1 to t3. At time t2, the communication terminal apparatus requests tochange the transmission method and modulation scheme, and at time t3,only the modulation scheme is changed from BPSK to 16QAM andtransmission method X and 16QAM are used from time t3 to t5.Furthermore, at time t4, the communication terminal apparatus requeststo change only the modulation scheme, and at time t5, only themodulation scheme is changed again from 16QAM to 64QAM. From time t5 tot6, transmission method X and 64QAM are used and at time t7, thecommunication ends.

Furthermore, when the base station apparatus and communication terminalapparatus start a communication at time t8, transmission method X andBPSK are forcibly used from time t9 to t11. At time t10, thecommunication terminal apparatus requests to change the transmissionmethod and modulation scheme, and at time t11, the transmission methodis changed from X to Y and the modulation scheme is changed from BPSK to16QAM and transmission method Y and 16QAM are used from time t11 to t13.Furthermore, at time t12, the communication terminal apparatus requeststo change only the modulation scheme, and at time t13, only themodulation scheme is changed again from 16QAM to QPSK. From time t13 tot14, transmission method Y and QPSK are used and at time t15, thecommunication ends.

In this way, using forcibly transmission method X and BPSK obtaininghigh error resistance and high reception quality at the start of acommunication the base station apparatus is capable of simplifying thecommunication procedure from the beginning of communication to datatransmission, and the communication terminal apparatus is capable ofreliably demodulating data immediately after the communication start.

Thus, according to this embodiment, the base station apparatus andcommunication terminal apparatus are provided with a plurality ofantennas respectively, forcibly applies at the start of a communicationany one of the transmission methods and modulation schemes having strongerror resistance out of a first transmission method transmitting a firstmodulated signal and second modulated signal including the same datafrom a plurality of antennas and a second transmission methodtransmitting a third modulated signal and a fourth modulated signalincluding different data from a plurality of antennas. And therefore, itis possible to simplify the communication procedure from the start ofthe communication to data transmission, and the communication terminalapparatus is capable of reliably demodulating the data immediately afterthe communication start. Furthermore, it is also possible to improve thedata transmission rate and transmission quality under an OFDM scheme.

This embodiment has explained the case where the transmission method andmodulation scheme are fixed at the start of a communication, but it isalso possible to fix only the transmission method and make themodulation scheme selectable.

Furthermore, this embodiment selects the transmission method andmodulation scheme based on reception quality such as a bit error rate,packet loss rate and frame error rate, but it is also possible to selectthe transmission method and modulation scheme based on eigenvalues ofthe channel matrix explained in Embodiment 1.

Embodiment 4

Embodiment 3 has explained the case where the transmission method ischanged only once during a communication without selecting thetransmission method and modulation scheme at the start of acommunication, but Embodiment 4 of the present invention will explain acase where a transmission method is changed at predetermined timeintervals during a communication.

Since the configurations of the base station apparatus and communicationterminal apparatus are the same as those in Embodiment 3, FIG. 17 andFIG. 18 will be used and detailed explanations thereof will be omitted.

FIG. 21 is a sequence diagram of a communication procedure of a basestation apparatus and communication terminal apparatus according toEmbodiment 4 of the present invention. Note that only ST1906 and ST1907in this figure are different from ST1606 and ST1607 in FIG. 19, and therest of the procedure is the same as that in FIG. 19. Therefore, onlyST1906 and ST1907 will be explained.

In ST1906, after a predetermined time passes from the start of acommunication, the communication terminal apparatus determines atransmission method and modulation scheme applied by the base stationapparatus and requests the determined contents from the base stationapparatus. The base station apparatus receives this request.

In ST1907, the base station apparatus determines the transmission methodand modulation scheme based on the request transmitted from thecommunication terminal apparatus and reports the determined transmissionmethod and modulation scheme to the communication terminal apparatususing transmission method report symbols.

FIG. 22 illustrates the transmission method and modulation schemeapplied by the base station apparatus changing with time-shift in such aseries of communication procedures. Here, three modulation schemes QPSK,16QAM, 64QAM are supposed to be used. In this figure, at time t0, acommunication between the base station apparatus and communicationterminal apparatus starts and from time t1 to t3, transmission method Xand BPSK are forcibly used. At time t2, the communication terminalapparatus requests to change the transmission method from X to Y and tochange the modulation scheme from BPSK to 16QAM, and from time t3 to t5,transmission method Y and 16QAM are used. Furthermore, at time t4, thecommunication terminal apparatus requests to change only the modulationscheme from 16QAM to 64QAM and from time t5 to t6, transmission method Yand 64QAM are used.

At time t6, the communication terminal apparatus requests to change thetransmission method and modulation scheme, requesting to change thetransmission method from Y to X, while to maintain the modulation schemeof 64QAM.

At time t7, the transmission method is changed during a communicationand from time t7 to t9, transmission method X and 64QAM are used.

At time t8, the communication terminal apparatus requests to change onlythe modulation scheme from 64QAM to 16QAM, and from time t9 to t11,transmission method X and 16QAM are used. Furthermore, at time t10, thecommunication terminal apparatus request to change only the modulationscheme from 16QAM to QPSK again, and from time t11 to t12, transmissionmethod X and QPSK are used and at time t13, and then the communicationends.

Thus, by changing the transmission method during a communication atpredetermined time intervals, it is possible to respond to a change ofthe propagation path model. Note that the predetermined time intervalsshould be such intervals that the transmission method is not changedunnecessarily.

In this way, according to this embodiment, when a communication takes along time, the propagation model may change. And by changing thetransmission method during the communication, it is possible to improveboth reception quality and the increase of transmission rate even whenthe propagation model changes during the communication.

Embodiment 3 and Embodiment 4 explains an OFDM scheme and the presentinvention is not limited to this and it is possible to add a spreadingsection and implement the present invention likewise under an OFDMscheme using a spread spectrum scheme. The present invention can also beimplemented under multicarrier schemes other than the OFDM scheme.

Embodiment 5

Embodiments 1 to 4 have explained the case where a scheme usingspace-time block codes or space-time trellis codes is used astransmission method X and a scheme for simultaneously transmitting aplurality of different data as shown in Equation (2) is used astransmission method Y. Embodiment 5 of the present invention willexplain a transmission method capable of obtaining a diversity gain suchas Cyclic Delay Diversity (CDD) as transmission method X which isdifferent from space-time block codes and space-time trellis codes.

Hereinafter, CDD will be explained using FIG. 23. FIG. 23 illustrates aframe configuration when CDD is carried out using 12 symbols. In thisfigure, transmission signal A and transmission signal B are framestransmitted from different antennas, for example, transmission signal Ais transmitted from antenna 202 shown in FIG. 4 and transmission signalB is transmitted from antenna 203 shown in FIG. 4.

Transmission signal A is made up of symbols Sy1, Sy2, . . . , Sy11, Sy12in that order used for CDD and the respective symbols are transmitted attimes i+1, i+2, . . . , i+11, i+12.

Transmission signal B is obtained by making a cyclic shift of 6 symbolsfrom a symbol sequence of transmission signal A and made up of Sy7, Sy8,. . . , Sy5, Sy6 in that order and the respective symbols aretransmitted at times i+1, i+2, . . . , i+11, i+12.

Adopting such a frame configuration allows an equalizer of the receptionapparatus to acquire a diversity gain and thereby improve data receptionquality. Therefore, though CDD has a lower transmission rate than thatof transmission method Y, but have better reception quality.

Therefore, Embodiments 1 to 4 can also be implemented using CDD as thetransmission method similar to space-time block codes or space-timetrellis codes.

Embodiment 6

Embodiment 5 has explained the scheme using CDD which is different fromspace-time block codes and space-time trellis codes as transmissionmethod X, Embodiment 6 of the present invention will further explain acase where a communication mode called an “eigenmode” in an MIMO(Multiple-Input Multiple-Output) system as transmission method X.

When channel state information which is a propagation channel estimationresult between both stations is already known not only to the receptionstation but also to the transmission station, the MIMO system canrealize a communication method whereby the transmission stationtransmits a signal vectorized using a transmission channel signaturevector to the reception station from a transmission array antenna andthe reception station detects and demodulates the transmission signalusing a reception channel signature vector associated with thetransmission channel signature vector from the received signal of thereception array antenna.

In this MIMO system, an eigenmode using singular vectors or eigenvectors of a channel matrix is available as a communication mode thatmultiplexes and transmits signals configuring a plurality of channels ina communication space (described, for example, in a document “Eigen BeamSpace Division Multiplexing (E-SDM) Scheme in MIMO Channel” Institute ofElectronics, information and Communication Engineers, TECHNICAL REPORTOF IEICE RCS2002-53, May 2002).

This eigenmode is a method of using these singular vectors and eigenvectors as channel signature vectors. Here, the channel matrix is amatrix whose elements consist of complex channel coefficients which area combination of some or all of antenna elements of a transmission arrayantenna and antenna elements of a reception array antenna.

FIG. 24 illustrates the configuration of a channel multiplexingcommunication system using a beam space mode represented by an eigenmodein an MIMO system. First, base station apparatus 2300 will be explained.Multiplexed frame generation section 2301 generates a plurality oftransmission frames for mapping a transmission data sequence input tomultiplexing channels and outputs the plurality of transmission framesgenerated to vector multiplexing section 2303.

Transmission channel analysis section 2302 calculates a plurality oftransmission channel signature vectors to constitute multiplexingchannels based on channel state information between base stationapparatus 2300 and communication terminal apparatus 2310. Transmissionchannel analysis section 2302 outputs the calculated transmissionchannel signature vectors to vector multiplexing section 2303.

Vector multiplexing section 2303 multiplies the respective transmissionframes output from multiplexed frame generation section 2301 bydifferent channel signature vectors output from transmission channelanalysis section 2302 and combines the transmission frames. Vectormultiplexing section 2303 transmits the combined signal to communicationterminal apparatus 2310 through transmission array antenna 2304.

Next, communication terminal apparatus 2310 will be explained. Receptionchannel analysis section 2311 calculates a plurality of receptionchannel signature vectors to separate the multiplexed transmissionsignal based on channel state information between base station apparatus2300 and communication terminal apparatus 2310. Reception channelanalysis section 2311 outputs the calculated plurality of receptionchannel signature vectors to multiplexed signal separation section 2313.

Multiplexed signal separation section 2313 generates a plurality ofreception frames by multiplying a signal (received signal) receivedthrough reception array antenna 2312 by the respective channel signaturevectors output from reception channel analysis section 2311. Multiplexedsignal separation section 2313 outputs a plurality of generatedreception frames to multiframe combination section 2314.

Multiframe combination section 2314 combines signals mapped to themultiplexing channels and obtains a received data sequence.

Here, assuming that base station apparatus 2300 has a function oftransmitting data by switching transmission method X and transmissionmethod Y, the configuration of the transmission apparatus provided forbase station apparatus 2300 is shown in FIG. 25. However, components ofFIG. 25 common to and FIG. 5 are assigned the same reference numeralsand detailed explanations thereof will be omitted.

In FIG. 25, when transmission method request information indicatestransmission method X, that is, an eigenmode, signal processing section2401 applies the above described signal processing using channel stateinformation from the other communication party (communication terminalapparatus 2310). On the other hand, when the transmission method requestinformation indicates transmission method Y, that is, the transmissionmethod shown in Equation (2), signal processing section 2401 does notapply any signal processing and outputs signal S5 as signal S110 andoutputs signal S9 to as signal S111.

Thus, using an eigenmode enables the reception apparatus to obtain goodreception quality in a reception environment in which direct waves aredominant. Therefore, it is also possible to implement Embodiments 1 to 4by using an eigenmode as a transmission method similar to space-timeblock codes and space-time trellis codes.

Embodiment 7

Embodiment 7 of the present invention will explain a method of switchingbetween the transmission method using an eigenmode explained inEmbodiment 6 and the transmission method shown in Equation (2).

Examples of generally known communication modes include a point-to-multipoint type communication mode shown in FIG. 26A, a point-to-point typecommunication mode shown in FIG. 26B and a point-to-point typecommunication mode shown in FIG. 26C.

FIG. 26A shows that a base station is communicating with a plurality ofcommunication terminals simultaneously and FIG. 26 shows that twocommunication terminals are communicating with each other. Likewise,FIG. 26C shows that a base station is communicating with onecommunication terminal.

However, the eigenmode has the following points that should be improved.First, since the eigenmode needs to acquire channel state informationfrom the other communication party, when the base station iscommunicating with a plurality of other communication parties, it isnecessary to acquire channel state information from the plurality of theother communication parties respectively, which deteriorates the datatransmission efficiency. Second, when eigen beams are formed for aplurality of other communication parties, it is necessary to performcomplicated signal processing.

For these reasons, in a point-to-multi point type communication mode inwhich there are a plurality of other communication parties, it is notdesirable to use eigenmode. Therefore, the eigenmode is preferably usedin a point-to-point type communication mode. That is, it is notnecessary to consider the points to be improved in above-mentionedeigenmode by using the eigenmode in the point-to-point typecommunication mode, and it is possible to increase the transmission rateand improve reception quality compared to the use of the transmissionmethod (transmission method Y) shown in Equation (2). However, when thetransmission method is changed according to the number of othercommunication parties, it is necessary to transmit the number of othercommunication parties with which the subject station is communicating tothe other communication parties, and therefore it is necessary to insertsymbol of “information on the number of other communication parties” inthe transmission frame.

After the transmission method is set, as explained in Embodiments 1 to4, it is possible to make compatible the data transmission rate with thetransmission quality by changing the modulation scheme. For the settingof the transmission method, the methods explained in Embodiments 1 to 4will be used.

Here, a further effect when the transmission method is changed accordingto the number of other communication parties as described above will beexplained using FIG. 27. As shown in FIG. 27, in a cell of a basestation which is communicating with two communication terminals A and B,two other communication terminals C and D can communicate in aneigenmode. This is because, according to the transmission method usingthe eigenmode, an eigen beam is formed directed to the othercommunication party, and therefore interference with the base stationand other communication terminals A and B can be avoided. However, asshown in FIG. 28, when communication terminals C and D carrying out acommunication using the eigenmode interfere with communication stations(base station, communication terminals A and B in FIG. 28) carrying outtransmission method Y, an interrupt mode that forcibly terminates acommunication using the eigenmode (eigen beam communication) can be setin a transmission signal of the base station.

Next, a communication procedure between the base station apparatus andthe communication terminal apparatus will be explained. FIG. 29illustrates a sequence diagram showing a communication procedure of thebase station apparatus and communication terminal apparatus. In thisfigure, in ST2801, the communication terminal apparatus requests thebase station apparatus to start communication and requests atransmission method (transmission method using an eigenmode ortransmission method shown in equation (2)) from the base stationapparatus, and the base station apparatus receives this request.Transmission method requested by the communication terminal apparatus isparticularly a transmission method using an eigenmode when thecommunication terminal apparatus desires a one-to-one (point-to-point,peer-to-peer) communication with the other communication party.

The base station apparatus then changes the transmission method inaccordance with the current communication mode. That is, the basestation apparatus changes the transmission method depending on whetheror not a one-to-multi point communication is being carried out. Morespecifically, the base station apparatus determines the transmissionmethod shown in Equation (2) when a one-to-multi point communication isbeing carried out and determines a transmission method using aneigenmode in the case of a communication with only the communicationterminal apparatus which has received the request (point-to-point type)and in ST2802, the base station apparatus reports the communicationterminal apparatus of the determined transmission method.

In ST2803, the communication terminal apparatus requests a modulationscheme suitable for the determined transmission method and the basestation apparatus receives this request.

In ST2804, the base station apparatus determines the modulation schemebased on the transmitted modulation scheme request information andnotifies the communication terminal apparatus of the determinedmodulation scheme.

In ST2805, the base station apparatus transmits data to thecommunication terminal apparatus using the transmission method notifiedin ST2802 and the modulation scheme notified in ST2804.

In ST2806, the communication terminal apparatus transmits data to thebase station apparatus using the communication scheme and modulationscheme used for data communication in ST2805.

In ST2807, the base station apparatus sends a report to end acommunication to the communication terminal apparatus, and thecommunication terminal apparatus receives this report, and thecommunication ends.

Thus, according to this embodiment, a transmission method using aneigenmode, which is transmission method X, is adopted in a one-to-onecommunication, and transmission method Y, a transmission method shown inEquation (2) is adopted in a one-to-multi point communication.Therefore, it is possible to improve both the data transmission rate andtransmission quality as the system.

The above described embodiments explains the communication terminalapparatus as an example of the reception apparatus and the base stationapparatus as an example of the transmission apparatus, but the presentinvention is not limited to this and the communication terminalapparatus may function as the transmission apparatus and the basestation apparatus may function as the reception apparatus. Furthermore,in the above described embodiments, the reception apparatus determinesthe transmission method and modulation scheme, but the present inventionis not limited to this and the transmission apparatus may determine thetransmission method and modulation scheme by receiving reports ofeigenvalues and reception field intensity from the reception apparatus.

Furthermore, in the above described embodiments, SyA and SyA* which is acomplex conjugate of SyA are transmitted as the data symbols to betransmitted using transmission method X, but the present invention isnot limited to this and SyA may be repeated and transmitted instead.

Furthermore, the above described embodiments explain assuming that thenumber of transmission antennas and the number of reception antennas are2 respectively, but the present invention is not limited to this andthree or more transmission antennas and reception antennas may be used.At this time, it goes without saying that the number of transmissionprocessing sections ahead of the antenna of the transmission apparatus(e.g., modulation section, spreading section, radio section andamplifier or the like) at the base station apparatus matches the numberof transmission antennas. The same applies to the reception apparatus atthe communication terminal apparatus. It is also possible to select anynumber of antennas from at least three antennas.

For example, the number of transmission antennas may be 4 and 4 lines ofmodulated signal may be transmitted from the 4 antennas. At this time,assuming that a method using space-time coding is transmission method Aand a method not using space-time coding is transmission method B, it ispossible to arbitrary select any one of transmission method X andtransmission method Y when two transmission antennas are use, and anyone of, transmission method A and transmission method B. Note that evenwhen the maximum value of the number of modulated M-ary index oftransmission method X and transmission method Y is greater than themaximum value of the number of modulated M-ary index of transmissionmethod A and transmission method B, there is no influence on thecomplexity of the circuit configuration of the communication terminalapparatus.

Furthermore, a plurality of antennas may be treated as one set ofantennas.

That is to say, there may be a plurality of antennas 202 and antennas203.

The transmission method of the present invention comprises atransmission method determining step of determining any one of a firsttransmission method whereby a transmission apparatus provided with aplurality of antennas transmits a plurality of signals including thesame data from a plurality of antennas and a second transmission methodwhereby the transmission apparatus transmits a plurality of signalsincluding different data from the plurality of antennas, a modulationscheme determining step of determining any one of the plurality ofmodulation schemes and a control step of controlling whether determiningprocessing should be performed or not in the transmission methoddetermining step and the modulation scheme determining step inaccordance with a communication procedure with the other communicationparty.

According to this method, it is possible to improve data transmissionefficiency by switching between the first transmission method havingstrong error resistance and the second transmission method having a highdata transmission rate and switching the modulation scheme in accordancewith the communication procedure with the other communication party.

In the above described transmission method of the present invention,control is performed in the control step so that determining processingis not carried out in the transmission method determining step duringdata transmission and determining processing is carried out only in themodulation scheme determining step.

According to this method, both the transmission method and modulationscheme are not determined, or changed during data transmission, whichrequires less processing compared to the case where both thetransmission method and modulation scheme are changed, and therefore itis possible to prevent a processing burden of the system increasing.

In the above described transmission method of the present invention, themodulation scheme used for the first transmission method and themodulation scheme used for the second transmission method have the samemaximum value of the number of modulated M-ary index.

According to this method, the amplitude variation range of the modulatedsignal becomes larger as the number of modulated M-ary index increases,and the power consumption of the corresponding amplifier becomes greateras the amplitude variation range of the modulated signal becomes larger.Therefore, by equalizing the maximum value of the number of modulatedM-ary index applied to both of the first transmission method and thesecond transmission method, it is possible to prevent power consumptionof the amplifier from increasing.

In the above described transmission method of the present invention, thefirst transmission method or the second transmission method aredetermined based on the channel fluctuation.

According to this method, since the second transmission method is likelyto deteriorate reception quality by receiving a direct wave, it ispossible to determine the first or second transmission method based onthe channel fluctuation, thereby avoid deterioration of receptionquality using the first transmission method when a direct wave isreceived and improve the data transmission efficiency using the secondtransmission method when a direct wave is not received.

In the above described transmission method of the present invention isdesigned to predetermine a transmission method to be used at the startof a communication in the transmission method determining step and amodulation scheme to be used at the start of a communication in themodulation scheme determining step.

According to this method, by forcibly applying the transmission methodand modulation scheme with strong error resistance at the start of acommunication, it is possible to simplify the communication procedurefrom the start of a communication to data transmission and reliablydemodulate the data immediately after the communication start on thereceiving side.

In the above described transmission method of the present invention,control in the control step is performed in such a way that determiningprocessing in the transmission method determining step is carried out atlonger time intervals than determining processing carried out in themodulation scheme determining step.

According to this method, the propagation model may change when thecommunication time extends, and therefore by changing the transmissionmethod at longer time intervals than changing the modulation scheme, itis possible to improve both reception quality and the increase of thetransmission rate even when the propagation model changes during thecommunication.

In the above described transmission method of the present invention isdesigned to use cyclic delay diversity as the first transmission methodin the transmission method determining step.

In the above described transmission method of the present invention isdesigned to use an eigenmode in which singular vectors or eigen vectorsof a channel matrix in an MIMO system are used as channel signaturevectors as the first transmission method in the transmission methoddetermining step.

According to these methods make it possible to improve data transmissionefficiency by adopting a transmission method using cyclic delaydiversity or eigenmode as the first transmission method.

In the above described transmission method of the present invention isdesigned to switch between the first transmission method and the secondtransmission method in accordance with the number of other communicationparties in the transmission method determining step.

According to this method, when the number of other communication partiesis, for example, 1, adopting the transmission method using an eigenmodecan reduce interference with other communication stations, and when thenumber of other communication parties is more than 1, adopting thesecond transmission method can prevent the data transmission efficiencydecreasing.

The communication system according to the present invention is a radiocommunication system comprising a transmission apparatus provided with aplurality of antennas and a reception apparatus that receives signalstransmitted from the plurality of antennas of the transmissionapparatus, wherein the reception apparatus comprises a channelfluctuation estimation section that estimates a channel fluctuationabout signals transmitted from the plurality of antennas of thetransmission apparatus, a transmission method requesting section thatdetermines any one of a first transmission method of transmitting aplurality of signals including the same data from the plurality ofantennas and a second transmission method of transmitting a plurality ofsignals including different data from the plurality of antennas based onthe estimated channel fluctuation and requests the determinedtransmission method from the transmission apparatus, a modulation schemerequesting section that determines any one of a plurality of modulationschemes based on the estimated channel fluctuation and requests thedetermined modulation scheme from the transmission apparatus and acontrol section that controls whether or not the processing requested bythe transmission method requesting section and modulation schemerequesting section should be performed in accordance with the procedurefor a communication with the transmission apparatus, and thetransmission apparatus comprises a generation section that generates asignal corresponding to the transmission method requested from thereception apparatus and a transmission processing section that modulatesa signal generated by the generation section according to the modulationscheme requested from the reception apparatus and transmits themodulated signal from the respective antennas.

According to this configuration, switching between the firsttransmission method having strong error resistance and the secondtransmission method having a high data transmission rate and switchingbetween modulation schemes are performed based on the estimation resultof the channel fluctuation estimation section, and therefore it ispossible to improve the data transmission efficiency and receptionquality.

The transmission apparatus of the present invention comprises aplurality of transmission antennas, a transmission method determiningsection that determines any one of a first transmission method oftransmitting a plurality of signals including the same data from theplurality of antennas and a second transmission method of transmitting aplurality of signals including different data from the plurality ofantennas, a modulation scheme determining section that determines anyone of a plurality of modulation schemes, a control section thatcontrols whether determining processing by the transmission methoddetermining section and modulation scheme determining section should beperformed or not in accordance with the procedure for a communicationwith the other communication party and a transmission processing sectionthat transmits the signals to which the determined transmission methodand modulation scheme are applied from the plurality of antennas.

According to this configuration, switching between the firsttransmission method with strong error resistance and the secondtransmission method with a high data transmission rate and switchingbetween the modulation schemes are performed in accordance with theprocedure for a communication with the other communication party, andtherefore it is possible to improve data transmission efficiency.

In the transmission apparatus of the present invention in the abovedescribed configuration, the control section controls in such a way thatthe transmission method determining section does not perform determiningprocessing during data transmission and only the modulation schemedetermining section performs determining processing.

According to this configuration, both the transmission method andmodulation scheme are not determined or changed during datatransmission, which requires less processing compared to the case whereboth the transmission method and modulation scheme are changed, and canthereby prevent a processing burden of the system from increasing.

In the transmission apparatus of the present invention in the abovedescribed configuration, the transmission processing section adopts amodulation scheme having the same maximum value of the number ofmodulated M-ary index for the modulation scheme used for the firsttransmission method and the modulation scheme used for the secondtransmission method.

According to this method, the amplitude variation range of the modulatedsignal becomes larger as the number of modulated M-ary index increases,and the power consumption of the corresponding amplifier becomes greateras the amplitude variation range of the modulated signal becomes larger.Therefore, by equalizing the maximum value of the number of modulatedM-ary index applied to both of the first transmission method and thesecond transmission method, it is possible to prevent power consumptionof the amplifier from increasing.

In the transmission apparatus of the present invention in the abovedescribed configuration, the transmission method determining section isconfigured predetermines the transmission method to be used at the startof a communication and the modulation scheme determining sectionpredetermines the modulation scheme to be used at the start of acommunication.

According to this configuration, by forcibly applying the transmissionmethod and modulation scheme with strong error resistance at the startof a communication, it is possible to simplify the communicationprocedure from the start of a communication to data transmission andreliably demodulate the data immediately after the communication starton the receiving side.

In the transmission apparatus of the present invention in the abovedescribed configuration, the control section is configured to control insuch a way that the transmission method determining section performsdetermining processing at longer time intervals than the modulationscheme determining section performs determining processing.

According to this configuration, the propagation model may change whenthe communication time extends, and therefore by changing thetransmission method at longer time intervals than changing themodulation scheme, it is possible to improve both reception quality andthe increase of the transmission rate even when the propagation modelchanges during a communication.

In the transmission apparatus of the present invention in the abovedescribed configuration, the transmission method determining section isconfigured to use cyclic delay diversity as the first transmissionmethod.

In the transmission apparatus of the present invention in the abovedescribed configuration, the transmission method determining section isconfigured to use an eigenmode in which singular vectors or eigenvectors of a channel matrix in an MIMO system are used as channelsignature vectors as the first transmission method.

According to these configurations, it is possible to improve datatransmission efficiency by adopting a transmission method using cyclicdelay diversity or eigenmode as the first transmission method.

In the transmission apparatus of the present invention in the abovedescribed configuration, the transmission method determining section isconfigured to switch between the first transmission method and thesecond transmission method in accordance with the number of othercommunication parties.

According to this configuration, when the number of other communicationparties is 1, adopting the transmission method using an eigenmode makesit possible to reduce interference with other communication stations,and when the number of other communication parties is more than 1,adopting the second transmission method makes it possible to prevent thedata transmission efficiency from decreasing.

The reception apparatus according to the present invention comprises atransmission method determining section that determines any one of afirst transmission method of transmitting a plurality of signalsincluding the same data from a plurality of antennas and a secondtransmission method of transmitting a plurality of signals includingdifferent data from the plurality of antennas, a modulation schemedetermining section that determines any one of a plurality of modulationschemes, a control section that controls whether or not the determiningprocessing by the transmission method determining section and modulationscheme determining section should be performed in accordance with theprocedure for a communication with the other communication party and arequesting section that requests the determined transmission method andmodulation scheme from the other communication party.

According to this configuration, switching between the firsttransmission method having strong error resistance and the secondtransmission method having a high data transmission rate and switchingbetween the modulation schemes in accordance with the procedure for acommunication with the other communication party, and therefore it ispossible to improve the data transmission efficiency.

In the reception apparatus of the present invention in the abovedescribed configuration, the control section performs control in such away that the transmission method determining section does not performdetermining processing during data reception and only the modulationscheme determining section performs determining processing.

According to this configuration, both the transmission method andmodulation scheme are not determined or changed during data reception,which requires less processing compared to the case where both thetransmission method and modulation scheme are changed, and therefore, itis possible to prevent a processing burden of the system fromincreasing.

The reception apparatus of the present invention in the above describedconfiguration comprises a channel fluctuation estimation section thatestimates both or any one of a channel fluctuation and reception fieldintensity of the received signal, wherein the transmission methoddetermining section determines the transmission method based on theestimation result estimated by the channel fluctuation estimationsection.

According to this configuration, the requesting section determines anyone of the first transmission method having strong error resistance andthe second transmission method having a high data transmission ratebased on the channel fluctuation estimated for the received signal orreception field intensity, and can thereby improve data transmissionefficiency and reception quality.

In the reception apparatus of the present invention in the abovedescribed configuration, the modulation scheme used for the firsttransmission method and the modulation scheme used for the secondtransmission method are configured to have the same maximum value of thenumber of modulated M-ary index.

According to this method, the amplitude variation range of the modulatedsignal becomes larger as the number of modulated M-ary index increases,and the power consumption of the corresponding amplifier becomes greateras the amplitude variation range of the modulated signal becomes larger.Therefore, by equalizing the maximum value of the number of modulatedM-ary index applied to both of the first transmission method and thesecond transmission method, it is possible to prevent power consumptionof the amplifier from increasing. Furthermore, the reception apparatusneed not process signals having a large amplitude variation range, andcan thereby simplify the circuit configuration.

According to the present invention, the transmission apparatus comprisesa plurality of antennas, determines any one of a first transmissionmethod of transmitting a plurality of signals including the same datafrom a plurality of antennas and a second transmission method oftransmitting a plurality of signals including different data from theplurality of antennas based on a channel fluctuation between thetransmitting and receiving sides and determines, when determining anyone of a plurality of modulation schemes, only a modulation scheme outof the transmission method and modulation scheme from the start to endof a communication, and therefore, it is possible to thereby improve thedata transmission rate and reception quality together.

This application is based on Japanese Patent Application No. 2003-188898filed on Jun. 30, 2003 and Japanese Patent Application No. 2004-190418filed on Jun. 28, 2004, entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a base station apparatusand communication terminal apparatus having a plurality of antennas.

1. A transmission method performed by a transmission apparatus having four antennas comprising: selecting a transmission scheme for transmitting a plurality of transmission signals among a plurality of transmission schemes according to a number of a plurality of antennas used for a transmission; selecting a modulation scheme among a plurality of modulation schemes according to the number of a plurality of antennas used for a transmission; modulating the plurality of transmission signals using the selected modulation scheme; outputting a plurality of modulated transmission signals; and transmitting the plurality of modulated transmission signals using the plurality of antennas used for the transmission among the four antennas, wherein the selecting a modulation scheme includes selecting, when the four antennas are used for the transmission, a modulating scheme in which a maximum value of a number of modulated M-ary index of the selected modulation scheme is smaller than a maximum value of a number of modulated M-ary index of the modulation scheme selected when two antennas among the four antennas are used for the transmission, and selecting, when the two antennas are used for the transmission, a modulating scheme having a same maximum value of a number of modulated M-ary index for the every selected transmission scheme.
 2. The transmission method according to claim 1, wherein the selecting a transmission scheme includes selecting, when the two antennas are used for the transmission, a transmission scheme using space-time block coding, a transmission scheme in which the plurality of transmission signals are multiplied and combined based on known information between the transmission apparatus and a reception apparatus, or a transmission scheme in which the two antennas transmits different transmission signals.
 3. The transmission method according to claim 1, wherein the selecting a transmission scheme includes selecting, when the four antennas are used for the transmission, a transmission scheme using space-time block coding, a transmission scheme in which the four antennas transmits different transmission signals, or a transmission scheme using Diversity transmission.
 4. The transmission method according to claim 1, wherein the transmitting includes amplifying the plurality of modulated transmission signals using a plurality of amplifiers having a same output characteristic.
 5. A transmission apparatus having four antennas comprising: a transmission and modulation scheme selection section that selects a transmission scheme for transmitting a plurality of transmission signals among a plurality of transmission schemes according to a number of a plurality of antennas used for a transmission, and selects a modulation scheme among a plurality of modulation schemes according to the number of a plurality of antennas used for a transmission; a modulation section that modulates the plurality of transmission signals using the selected modulation scheme and outputs a plurality of modulated transmission signals; and a transmission section that transmits the plurality of modulated transmission signals using the plurality of antennas used for the transmission among the four antennas, wherein the transmission and modulation scheme selection section selects, when the four antennas are used for the transmission, a modulating scheme in which a maximum value of a number of modulated M-ary index of the selected modulation scheme is smaller than a maximum value of a number of modulated M-ary index of the modulation scheme selected when two antennas among the four antennas are used for the transmission, and selects, when the two antennas are used for the transmission, a modulating scheme having a same maximum value of a number of modulated M-ary index for the every selected transmission scheme.
 6. The transmission apparatus according to claim 5, wherein, when the two antennas are used for the transmission, the transmission and modulation scheme selection section selects a transmission scheme using space-time block coding, a transmission scheme in which the plurality of transmission signals are multiplied and combined based on known information between the transmission apparatus and a reception apparatus, or a transmission scheme in which the two antennas transmits different transmission signals.
 7. The transmission apparatus according to claim 5, wherein, when the four antennas are used for the transmission, the transmission and modulation scheme selection section selects a transmission scheme using space-time block coding, a transmission scheme in which the four antennas transmits different transmission signals, or a transmission scheme using Diversity transmission.
 8. The transmission apparatus according to claim 5, wherein the transmission section amplifies the plurality of modulated transmission signals using a plurality of amplifiers having a same output characteristic. 